1. Field of the Invention
The present invention relates to apparatus and processes for packaging microelectronic dice. In particular, the present invention relates to a packaging technology that encapsulates a microelectronic die within a heat spreader.
2. State of the Art
Higher performance, lower cost, increased miniaturization of integrated circuit components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. As these goals are achieved, microelectronic dice become smaller. Of course, the goal of greater packaging density requires that the entire microelectronic die package be equal to or only slightly larger (about 10% to 30%) than the size of the microelectronic die itself. Such microelectronic die packaging is called a xe2x80x9cchip scale packagingxe2x80x9d or xe2x80x9cCSPxe2x80x9d.
As shown in FIG. 27, true CSP would involve fabricating build-up layers directly on an active surface 204 of a microelectronic die 202. The build-up layers may include a dielectric layer 206 disposed on the active surface 204 and conductive traces 208 may be formed on the dielectric layer 206, wherein a portion of each conductive trace 208 contacts at least one contact 212 on the active surface 204. External contacts, such as solder balls or pins for contacting an external devices (not shown), may be fabricated to contact at least one conductive trace 208. FIG. 27 illustrates the external contacts as solder balls 214 which are surrounded by a solder mask material 216 on the dielectric layer 206. However, the surface area provided by the active surface 204 generally does not provide enough surface for all of the external contacts needed to contact the external device (not shown) for certain types of microelectronic dice (e.g., logic).
Additional surface area can be provided with the use of an interposer, such as a substantially rigid material or a substantially flexible material. FIG. 28 illustrates a substrate interposer 222 having a microelectronic die 224 attached to and in electrical contact with a first surface 226 of the substrate interposer 222 through solder balls 228. The solder balls 228 extend between contacts 232 on the microelectronic die 224 and conductive traces 234 on the substrate interposer first surface 226. The conductive traces 234 are in discrete electrical contact with bond pads 236 on a second surface 238 of the substrate interposer 222 through vias 242 that extend through the substrate interposer 222. External contacts 244 are formed on bond pads 236. The external contacts 244 are utilized to achieve electrical communication between the microelectronic die 224 and an external electrical system (not shown).
The use of the substrate interposer 222 requires number of processing steps which increase the cost of the package. Additionally, the use of the small solder balls 228 presents crowding problems which can result in shorting between the small solder balls 228 and can present difficulties in inserting underfill material between the microelectronic die 224 and the substrate interposer 222 to prevent contamination and provide mechanical stability. Furthermore, the necessity of having two sets of solder balls (i.e., small solder balls 228 and external contacts 244) to achieve connection between the microelectronic die 224 and the external electrical system decreases the overall performance of the package.
Another problem arising from the fabrication of a smaller microelectronic die is that the density of power consumption of the integrated circuit components in the microelectronic die has increased, which, in turn, increases the average junction temperature of the die. If the temperature of the microelectronic die becomes too high, the integrated circuits of the semiconductor die may be damaged or destroyed. Furthermore, for microelectronic dice of equivalent size, the overall power increases which presents the same problem of increased power density.
Various apparatus and techniques have been used for removing heat from microelectronic dice. One such heat dissipation technique involves the attachment of a heat sink to a microelectronic die. FIG. 29 illustrates an assembly 250 comprising a microelectronic die 252 physically and electrically attached to a substrate carrier 254 by a plurality of solder balls 256. A heat sink 258 is attached to a back surface 262 of the microelectronic die 252 by a thermally conductive adhesive 264. The heat sink 258 is usually a slug constructed from a thermally conductive material, such as copper, copper alloys, aluminum, aluminum alloys, and the like. Heat generated by the microelectronic die 252 is conductively drawn into the slug-type heat sink 258 (following the path of least thermal resistance) and convectively dissipated from the slug-type heat sink 258 into the air surrounding the heat sink assembly 250. Thus, as the size or xe2x80x9cfootprintxe2x80x9d of microelectronic dice decreases, the contact area between the micro-electronic die 252 and the heat sink 258 decreases, which reduces the area available for conductive heat transfer. Thus, with a decrease of the size in the microelectronic die 252, heat dissipation from a slug-type heat sink 258 becomes less efficient.
Therefore, it would be advantageous to develop new apparatus and techniques to provide additional surface area to form traces for use in CSP applications, eliminate the necessity of the substrate interposer, and provide improved heat dissipation.